The invention relates to an arrangement for fastening and protecting a capacitor, the arrangement allowing a capacitor to be fastened to a place of installation and protected from stress caused by the environment.
Such a fastening and protection arrangement can be used in an electrotechnical device, for example for fastening the capacitors in a frequency converter to the attaching parts of the device and for protecting the capacitors from stress caused by the environment, such as moisture.
It is previously known to fasten capacitors comprised by a device to a clip plate by means of different fasteners, such as clips, collars or screws. A known fastening method comprises a bolt that is fastened to a capacitor, usually to the end opposite to its poles, and from which the capacitor is fastened with nuts to a clip plate underneath it.
However, such prior art fastening solutions are problematic, since a suitably sized fastener always has to be available or, for screw fastening, a screw has to be attached or attachable to the capacitor. Furthermore, technically, from the point of view of installation, such fastening is time-consuming. Also, prior art fastening solutions do not protect the capacitor at all from stress caused by the environment, such as moisture, dust, gases or the like.
The object of the present invention is to eliminate prior art drawbacks and to provide a novel solution for fastening a capacitor to an electrotechnical device, which solution also protects the capacitor efficiently against stress caused by the environment.
This is achieved by an arrangement for fastening and protecting a capacitor in accordance with the present invention having the characteristics defined in the claims. More exactly, the arrangement of the invention is mainly characterized by what is stated in the characterizing part of claim 1.
The preferred embodiments of the invention are disclosed in the dependent claims.
The basic idea of the invention is to accommodate a capacitor to a cuplike fastening and protection means, which is fastened to an attaching part of an electric device, such as a clip plate. This way the fastening and protection means preferably simultaneously acts as a fastener for the capacitor, i.e. when installed in place in the fastening and protection means, the capacitor remains in position in its place of installation. Secondly, the fastening and protection means resting against the outer surface of the casing of the capacitor protects the capacitor efficiently against environmental stress. The fastening and protection means is made from a dielectric gastight and water-tight material, such as plastic or a corresponding polymer, whereby the fastening and protection means of the invention preferably constitutes an electric insulation and a gastight and watertight insulation around the capacitor. Furthermore, the fastening and protection means tends to prevent the capacitor parts from spreading and an electric arc from being generated within the casing of the electric device, should the capacitor for some reason blow into pieces because of an electric interference impulse.
The arrangement of the invention provides a plurality of advantages. The fastening and protection means of the invention can be made simply and inexpensively for example by molding a suitable plastic.
The casing of the fastening and protection means preferably comprises only one opening, i.e. an opening from which the capacitor is accommodated to the inside of the fastening and protection means. This renders the means tight and efficiently insulating.
A fastening collar is provided close to the opening on the outer surface of the casing of the fastening and protection means. The fastening collar enables easy installation and fastening of the fastening and protection means to the attaching parts of the electric device, since the fastening collar preferably supports the fastening and protection means in the opening of the attaching part. This is achieved by dimensioning the fastening collar substantially broader than the diameter of the outer surface of the casing of the fastening and protection means.
One or more fastening elements for fastening the fastening and protection means to the attaching part of the electric device are provided in the fastening collar. Such a fastening element is preferably a fastening lug provided with an opening for receiving a connecting means, such as a screw, by means of which the fastening and protection means is arranged to be fastened to the attaching part of the electric device. The one or more fastening elements provided in the fastening collar are disposed asymmetrically in the fastening collar. This provides the significant advantage that the fastening and protection means, in which a capacitor is preferably already arranged, can be fastened to the attaching part of the electric device only in a certain direction, whereby a backwards electric coupling of the capacitor can be preferably eliminated thus eliminating damage to it during installation.
The diameter of the inner surface of the casing of the fastening and protection means is preferably dimensioned such that the capacitor fits tightly against the inner surface of the casing when placed in the fastening and protection means. Such tight fitting provides significant advantages in cooling a capacitor, since no heat-insulating air gap remains between the casing of the capacitor and the fastening and protection means, but heat is allowed to efficiently pass to the cooling air, gas or liquid flowing outside the fastening and protection means through the casing of the fastening and protection means.
The fastening collar of the fastening and protection means and the attaching part of the electric device are arranged to provide a tight joint surface. This is achieved by dimensioning the outer surface of the casing of the fastening and protection means exactly equal to the diameter of the fastening opening pierced in the attaching part of the device and by dimensioning the fastening collar substantially larger than the diameter of the fastening opening pierced to the attaching part of the device. This allows tight housing structures to be preferably created in the device by suitably arranging the fastening and protection means and the attaching parts of the device, some of the housing structures acting as dry spaces and some as wet spaces, in which more moisture is allowed than in the dry spaces. Depending on environmental conditions, the protection rating of dry spaces includes standard ratings up to protection rating IP65. If the tightness of the insulation is to be further improved, a seal material piece may be arranged between the fastening collar of the fastening and protection means and the attaching part of the device.
Since the designs of capacitors are often cylindrical, the structure of the fastening and protection means is preferably designed substantially cylindrical.
The use of the fastening and protection means of the invention allows the steps of capacitor installation to be reduced, resulting in a more inexpensive, faster and improved installation and a high-quality product, such as a frequency converter.